Properties of Water
Water is special!
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The unique properties of water make life possible
on Earth and are a direct result of its polarity.
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Remember: Polarity is the unequal sharing of electrons.
Eight protons in nucleus creates stronger attraction for e-.
Greater probability of shared e-s near oxygen atom.
Polarity creates hydrogen bonds and
many special properties
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Polar molecules attract each other because of
their partial charges.
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Create hydrogen bonds between molecules.
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.
Not as strong as covalent or ionic bonds
Hydrogen Bonding
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Intermolecular (between)
bonding
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H from one water
molecule forms bond with
oxygen of another
molecule
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Weak bonds—easily
broken
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Jumping in a pool
Basilisk video
Polarity creates hydrogen bonds and
many special properties
• Cohesion
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Attraction between molecules of the same substance.
Surface tension.
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Cohesive forces hold surface molecules tightly, creating an elastic-like layer across
the surface.
Polarity creates hydrogen bonds and
many special properties
• Cohesion
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Attraction between molecules of the same substance.
Surface tension.
• Adhesion
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Attraction between molecules of different substances.
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ie~ graduated cylinder
Adhesion, Cohesion,
Surface Tension
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Adhesion: water + other polar molecules
Cohesion: water + water
Capillary action: adhesion + cohesion
Surface Tension: cohesion at the surface
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organisms (water striders) can move across the water’s
surface
Solutions & Suspensions
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Water is often found as a mixture.
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Composed of two or more elements.
Physically mixed but not chemically combined.
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Two types can be made with water:
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Solutions
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Ex: salt & pepper; air
Compounds evenly distributed throughout.
Solute vs solvent
Suspensions
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Water + nondissolved material.
Solvent Power
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Water is often called the “universal
solvent”.
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Polarity allows it to dissolve both ionic &
polar compounds.
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Ions on the surface of the compound are
attracted to polar water molecules.
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Water dissolve substances by
surrounding charged particles and
"pulling" them into solution.
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Ions of compound become universally
dispersed.
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What do
you notice
about the
way the
poles of
water line
up?
Use your textbook to review! See Figure 2-9
Dissociation of Salt
Water Resists Temperature Change
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High heat of vaporization (lots of heat to turn to
vapor!)
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Because:
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Hydrogen Bonds
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Need energy to break apart H-bonds before phase change.
Water Resists Temperature Change
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Sweating: water can absorb a lot of heat
through evaporative cooling.
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Within the human body: maintain temperature
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75 % water
Water can moderate the Earth’s temperature.
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Oceans
Humidity
Ice vs. Water
Which is more dense?
Ice vs. Water
Which is more dense?
• Ice floats
because the
density of ice is
less than cold
water.
Water is Less Dense as a Solid
• Water molecules spread out as they freeze to
form a crystal structure; ice takes up more space!
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In ice, water molecules crystallize and form stable hydrogen
bonds that are spread out
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In liquid, water molecules move past each other in a tightly
packed formation
Water: Summary
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Polarity creates hydrogen bonds which give water
many special properties.
Can you:
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Draw a water molecule, show polarity
List several properties of water
Describe why hydrogen bonds form between water molecules
Describe experiments that demonstrate each property
Compare and contrast Cohesion and Adhesion
APPLY understanding to living things: Why is it important in
living things that water is more dense than ice? Where does
capillary action occur in living things? What substances are
dissolved in our body fluids?